Popular Mechanics Senior Editor Joe Pappalardo is at the home of JPL, where the scientists who built Mars Science Lab and its Curiosity rover anxiously await the landing.

UPDATE: The JPL headquarters erupted in elation this morning (Eastern time) as word came back that Curiosity had successfully landed on Mars. The control room had drawn eerily quiet as the MSL team waited for word from the Red Planet, but the complex guided entry went exactly as planned. The rover beamed back to small images of its wheels and its shadow on Mars.

Pasadena, Calif.—If Steven Lee is nervous about the impending landing of the Mars Science Laboratory, he's hiding it well.

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Lee has a lot at stake tonight. He has been with the MSL program for 7 years, working on the entry, descent, and landing hardware that will, for the first time, conduct a guided landing on the red planet.

"I might seem composed and confident but there's always something inside that is nervous," he says, sitting on a bench outside the JPL mission headquarters here in Pasadena. This whole place is steeped in aerospace lore. The bench, he says, is where Carl Sagan came up with the idea for the TV series Cosmos.

Tonight is his turn to make space history. At about 1:30 a.m. Eastern time, MSL will reach Mars.

Mars is a probe-killer; only one third of the robots sent there survived to the surface. An entry that relies just on ballistic calculations would give a 120 mile landing area. But the ability to stick a pinpoint landing cuts down the time and risk associated with driving around the surface, so Lee's team developed hardware that will allow MSL to land at a specific place, within 12 miles.

Guided entry has not been done on Mars, but it was done on the Moon. The equations had to be altered to account for the Martian atmosphere and other parameters, but the architecture is the same. "We used algorithms developed during the Apollo era," Lee says. "At the start of the program we had Apollo engineers come in to advise us."

Another critical piece of hardware that enables a guided landing is the radar, which scans the surface to get a location of the descending craft. Lee, who was in charge of developing it, says the 1.5 meter dish has 6 flat antenna, each pointed in strategic directions to cover the landing in X-band pulse Doppler radar. The antenna beam in cycles, independent of each other and divorced even from their earlier data. That way, in case one of the antenna provides an erroneous data (such as bouncing off the heat shield after it jettisons, instead of the ground), it won't affect future calculations.

Lee's team installed the radar on a helicopter and tested it over desert environments like Death Valley. For tests in altitudes higher than helicopters can operate (over 10,000 feet) the scientists installed the radar in an F/A-18 and flew it inside a radome in maneuvers at Dryden test center.

"One reason I am so composed is that we resisted the temptation to jump right into simulations," Lee says. The idea, he says, is to test every component on prototypes and then build a simulation that integrates each into the landing scenario. "Tonight is the validation of our simulations," Lee says. "Unfortunately, it comes with a $2.5 billion price tag."

After MSL lands, Lee will transition to the ground operations team and his life will be on Mars time. "I'll get about two hours sleep. My shift starts tomorrow," he says, smiling.